(1) Field of the Invention
The present invention relates to nickel electrode active material; a nickel electrode and a nickel alkali storage cell using such nickel electrode active material; and production methods of such material, electrode, and cell. Specifically, it relates to improvement of the nickel active material used for the nickel alkali storage cell.
(2) Prior Art
Recently, in the rapid spread of portable apparatus, a storage cell of high efficiency is in increasing demand.
In this background, there has been various improvement in a nickel positive electrode for a nickel alkali storage cell. One of the examples is disclosed in Japanese Patent Publication No. 6-38336, which is about how to keep the volume of holes less than 0.05 ml/g by limiting the development of internal transition pores whose radiuses are more than 30 .ANG., in time of producing nickel hydroxide powder which is used as active material for a nickel positive electrode. According to this prior art, nickel hydroxide is changed to high-density nickel hydroxide powder. When this high-density nickel hydroxide powder is used as active material, packing density on the electrode substrate is increased, so that energy density of the electrode can be improved. And in a nickel hydroxide electrode in which the high-density nickel hydroxide powder is packed, production of .gamma.-NiOOH (oxide having high oxidation number) accompanied by the progress of charge and discharge cycle is little. So passivation of nickel active material is controlled, and the utilization factor improves. Therefore, cell capacity of the nickel alkali storage cell can be improved.
However, consideration was not given enough to each of the fine-grained active material. There are some points to be improved in the utilization factor of the active material and over discharge characteristics. In the prior art, it was difficult to obtain values over 90% in the utilization factor and over discharge characteristics while method of measurement mentioned later is being employed.